1. Field of the Invention
The present invention relates to imaging devices and, more particularly, relates to an imaging device capable of displaying a moving picture image, which is generated by a camera that photographs an object to be inspected, on a mosaic image that is wider in field of view than an actual field of view of the camera.
2. Description of the Related Art
An image mosaic is known in the related art as a technique which creates a sheet of an image with a wide field of view that is wider in field of view than an actual field of view of a camera by assembling a plurality of still images photographed while changing a field of view. In the case of an imaging device such as an enlarging observation device which photographs a photographic subject enlarged by an objective lens, a field of view can be changed by moving a movable stage on which an object to be inspected is mounted. The image with a wide field of view is called as a mosaic image, and is created by coupling the plurality of still images photographed while changing the field of view in such a manner based on a relative position between images.
For example, in the case of the known imaging device which is equipped with a sensor that detects a position of a movable stage and automatically photographs a photographing range specified by a user, a relative positional relationship between images is judged by control information of the movable stage, and assembly of still images is performed. In such imaging device, when the photographing range is specified and photographing is once started, the photographing range cannot be changed in mid-flow. Furthermore, the position of the movable stage needs to be highly accurately detected; and therefore, there is a problem in that system configuration becomes complicated and high cost.
On the other hand, there is also an imaging device which judges a relative positional relationship between images by pattern matching between the images and assembly of still images is performed. However, there is not an imaging device capable of fetching still images and coupling the same with a mosaic image while making a user confirm a positional relationship between a field of view during photographing and the mosaic image during creation on a display unit. Consequently, there is conceivable an imaging device in which still images are fetched at timing specified by a user and are assembled to a mosaic image while displaying a field of view during photographing as a moving image on the mosaic image.
Furthermore, there is known a technique which photographs a plurality of still images while changing a focal position of a camera, combines these still images, and accordingly creates an omnifocal image and surface shape data. The omnifocal image is deeper in depth of field than an actual field of view of the camera and a composite image that comes into focus in the whole of the field of view. The omnifocal image is created by comparing pixel values between the plurality of the still images different in focal position and by extracting a pixel value of a focal position that comes into focus. On the other hand, the surface shape data is difference in height information showing concavity and convexity or step of the surface of an object to be inspected, and is created by comparing the pixel values between the still images and by determining the focal position that comes into focus.
Generally, in the omnifocal image and the surface shape data, a range that comes into focus, that is, larger concavity and convexity or step than depth of field can be identified. Therefore, the smaller the range that comes into focus is, the higher quality the image data is able to be obtained; however, an actual field of view of a camera becomes narrow. Consequently, if a plurality of the omnifocal images created in such a manner are assembled, the omnifocal image with a wide visual field can be obtained as a mosaic image. However, in order to display a field of view during photographing as a moving picture image at an appropriate position on such a mosaic image, when it is tried to perform positioning of a frame image by pattern matching between images, there is a problem in that the positioning cannot be sometimes performed due to an out-of-focus blur in an overlap portion. As a method of eliminating the out-of-focus blur in the overlap portion, there is conceivable a method which uses a function for changing a focal position of the camera in a predetermined range and searching the focal position that comes into focus, that is, a method which uses an auto focusing function. However, in this method, when a frame image is positioned, the camera needs to be controlled to change the focal position, and the focal position capable of positioning has to be searched by performing pattern matching each time the focal position is changed; and therefore, there is a problem in that a time necessary for positioning becomes long.